Compression control of cascode power amplifiers

ABSTRACT

Compression control of cascode power amplifiers. A power amplifier module can include a power amplifier including a cascode transistor pair. The cascode transistor pair can include a first transistor and a second transistor. The power amplifier module can include a current comparator configured to compare a first base current of the first transistor and a second base current of the second transistor to generate a comparison signal. The power amplifier module can include a saturation controller configured to maintain the power amplifier out of saturation based on the comparison signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.14/867,264, filed Sep. 28, 2015, entitled COMPRESSION CONTROL THROUGHPOWER AMPLIFIER VOLTAGE ADJUSTMENT, which application claims priority toU.S. Provisional Application No. 62/097,877, filed Dec. 30, 2014,entitled COMPRESSION CONTROL THROUGH POWER AMPLIFIER LOAD ADJUSTMENT,U.S. Provisional Application No. 62/097,899, filed Dec. 30, 2014,entitled COMPRESSION CONTROL THROUGH AMPLITUDE ADJUSTMENT OF A RADIOFREQUENCY INPUT SIGNAL, and U.S. Provisional Application No. 62/097,941,filed Dec. 30, 2014, entitled COMPRESSION CONTROL THROUGH POWERAMPLIFIER VOLTAGE ADJUSTMENT, the disclosure of each of which is herebyexpressly incorporated by reference herein in its entirety.

BACKGROUND

Field

The present disclosure generally relates to wireless communicationsystems having a cascode power amplifier.

Description of the Related Art

Many wireless devices include one or more linear power amplifiers. Inorder for the power amplifier to accurately amplify the received signal,it is desirable to avoid compression of the signal. When the poweramplifier compresses the signal, the power amplifier output may nolonger be linearly related to its input and the modulated waveform maybecome distorted. Further, the signal spectrum may change and start todegrade causing spectrum to spread into adjacent areas of the band andviolate system specifications. The spreading of the spectrum intoadjacent channels can interfere with other wireless devices therebynegatively impacting other wireless devices.

SUMMARY

In accordance with some implementations, the present disclosure relatesto a power amplifier module including a power amplifier. The poweramplifier includes a cascode transistor pair. The cascode transistorpair includes a first transistor and a second transistor. The poweramplifier module includes a power amplifier bias controller. The poweramplifier bias controller includes a current comparator configured tocompare a first base current of the first transistor and a second basecurrent of the second transistor to obtain a comparison value. The poweramplifier module includes a saturation controller configured to supply areference signal to an impedance matching network based on thecomparison value. The impedance matching network is configured to modifya load impedance of a load line in electrical communication with thepower amplifier based at least in part on the reference signal.

In some embodiments, the first transistor can be a common basetransistor and the second transistor can be a common emitter transistor.

In some embodiments, the load line can be in electrical communicationwith an antenna and the load line can be electrically located betweenthe power amplifier and the antenna.

In some embodiments, the impedance matching network can be a dynamicimpedance matching network.

In some embodiments, the saturation controller can be further configuredto reduce compression of the power amplifier by modifying the loadimpedance of the load line.

In some embodiments, the saturation controller can further include adigital-to-analog converter and a ramp generator. The ramp generator canbe configured to supply a count value to the digital-to-analog converterand the digital-to-analog converter can be configured to generate thereference signal based at least in part on the count value.

In some embodiments, the saturation controller can include a pull-downresistor in electrical communication with the power amplifier biascontroller, a voltage input/output pin and a ramp clock generator. Theramp clock generator can be configured to detect whether the firsttransistor is operating in a saturation region based on a voltage acrossthe pull-down resistor. The voltage can be based at least in part on thecomparison value. In response to detecting that the first transistor isoperating in the saturation region, the ramp clock generator can beconfigured to cause the ramp generator to modify the count value.

In some embodiments, the digital-to-analog converter can be furtherconfigured to generate the reference signal based at least in part on anaverage power tracking value determined based on a target power signalreceived from a base station.

In some embodiments, the saturation controller can further include a RFfront end configured to receive a default data value from a saturationdata pin. The count value can initially correspond to the default datavalue. In some embodiments, the default data value can be one of aplurality of default data values and can be selected based on a targetvoltage. In some embodiments, the target voltage can be determined basedat least in part on a target power signal received from a base station.

In some embodiments, the power amplifier module can further include aboost converter configured to regulate a supply voltage provided to thepower amplifier. In some embodiments, the saturation controller can befurther configured to reduce compression of the power amplifier by acombination of providing a second reference signal to the boostconverter to increase the supply voltage and modifying the loadimpedance of the load line by supplying the reference signal to theimpedance matching network.

In accordance with some implementations, the present disclosure relatesto a transceiver including an impedance matching network. The impedancematching network is configured to modify, based on a reference signal, aload impedance of a load line in electrical communication with a poweramplifier and an antenna. The transceiver further includes a poweramplifier module including the power amplifier, a power amplifier biascontroller, and a saturation controller. The power amplifier includes acascode transistor pair. The cascode transistor pair includes a firsttransistor and a second transistor. The power amplifier bias controllerincludes a current comparator configured to compare a base current ofthe first transistor and a base current of the second transistor toobtain a comparison value. The saturation controller is configured togenerate the reference signal based at least in part on the comparisonvalue and to provide the reference signal to the impedance matchingnetwork.

In some embodiments, the impedance matching network can be a dynamicimpedance matching network.

In some embodiments, the saturation controller can further include adigital-to-analog converter and a ramp generator. The ramp generator canbe configured to supply a count value to the digital-to-analog converterand the digital-to-analog converter can be configured to generate thereference signal based at least in part on the count value.

In some embodiments, the saturation controller can include a pull-downresistor in electrical communication with the power amplifier biascontroller, a voltage input/output pin, and a ramp clock generator. Theramp clock generator can be configured to detect whether the firsttransistor is operating in a saturation region based on a voltage acrossthe pull-down resistor, the voltage based at least in part on thecomparison value and, in response to detecting that the first transistoris operating in the saturation region, configured to cause the rampgenerator to modify the count value.

In some embodiments, the transceiver further includes a boost converterconfigured to regulate a supply voltage provided to the power amplifier.In some embodiments, the saturation controller is further configured toreduce compression of the power amplifier by a combination of providinga second reference signal to the boost converter to increase the supplyvoltage and modifying the load impedance of the load line by supplyingthe reference signal to the impedance matching network.

In accordance with some implementations, the present disclosure relatesto a wireless device including an antenna configured to at leasttransmit a signal from a transceiver, the signal based at least in parton a radio frequency input signal supplied to a power amplifier of thetransceiver. The transceiver includes an impedance matching network anda power amplifier module. The impedance matching network is configuredto modify, based on a reference signal, a load impedance of a load linein electrical communication with the power amplifier and the antenna.The power amplifier module includes the power amplifier, a poweramplifier bias controller, and a saturation controller. The poweramplifier includes a cascode transistor pair. The cascode transistorpair includes a first transistor and a second transistor. The poweramplifier bias controller includes a current comparator configured tocompare a base current of the first transistor and a base current of thesecond transistor to obtain a comparison value. The saturationcontroller is configured to generate the reference signal based at leastin part on the comparison value and to provide the reference signal tothe impedance matching network.

In accordance with some implementations, the present disclosure relatesto a power amplifier module including a power amplifier. The poweramplifier includes a cascode transistor pair. The cascode transistorpair includes a first transistor and a second transistor. The poweramplifier module includes a power amplifier bias controller. The poweramplifier bias controller includes a current comparator, a saturationcontroller, and a radio frequency (RF) attenuator. The currentcomparator is configured to compare a first base current of the firsttransistor and a second base current of the second transistor to obtaina comparison value. The saturation controller is configured to supply areference signal to the RF attenuator based on the comparison value. TheRF attenuator is configured to modify the amplitude of an RF inputsignal supplied to the power amplifier based at least in part on thereference signal.

In some embodiments, the RF attenuator can be a digital attenuatorconfigured to modify the amplitude of the RF input signal based at leastin part on an attenuation value. In some embodiments, the attenuationvalue can be a discrete attenuation value selected from a plurality ofdiscrete attenuation values. Selection of the discrete attenuation valuecan be based at least in part on the reference signal.

In some embodiments, the RF attenuator can be an analog attenuatorconfigured to modify the amplitude of the RF input signal based at leastin part on an attenuation value. In some embodiments, the attenuationvalue can be based on an analog voltage that is continuously modifieduntil the reference signal indicates that the power amplifier is notoperating in a saturated state. In some embodiments, the analogattenuator can determine whether to modify the analog voltage byincreasing the analog voltage or decreasing the analog voltage based atleast in part on a polarity of the analog attenuator.

In some embodiments, the first transistor can be a common basetransistor and the second transistor can be a common emitter transistor.

In some embodiments, the power amplifier module can include a boostconverter configured to regulate a supply voltage provided to the poweramplifier.

In some embodiments, the saturation controller can further include adigital-to-analog converter and a ramp generator. The ramp generator canbe configured to supply a count value to the digital-to-analogconverter. The digital-to-analog converter can be configured to generatethe reference signal based at least in part on the count value.

In some embodiments, the reference signal can be an 8-bit word thatspecifies an attenuation value for the RF attenuator. The RF attenuatorcan modify the amplitude of the RF input signal based at least in parton the attenuation value.

In some embodiments, the saturation controller can include a pull-downresistor in electrical communication with the power amplifier biascontroller, a voltage input/output pin, and a ramp clock generator. Theramp clock generator can be configured to detect whether the firsttransistor is operating in a saturation region based on a voltage acrossthe pull-down resistor. The voltage can be based at least in part on thecomparison value. In response to detecting that the first transistor isoperating in the saturation region, the ramp clock generator can beconfigured to cause the ramp generator to modify the count value.

In accordance with some implementations, the present disclosure relatesto a transceiver comprising a receiver and a transmitter. Thetransmitter includes a power amplifier module. The power amplifiermodule includes a power amplifier and a power amplifier bias controller.The power amplifier includes a cascode transistor pair. The cascodetransistor pair includes a first transistor and a second transistor. Thepower amplifier bias controller includes a current comparator, asaturation controller, and a radio frequency (RF) attenuator. Thecurrent comparator is configured to compare a base current of the firsttransistor and a base current of the second transistor to obtain acomparison value. The saturation controller is configured to supply areference signal to the RF attenuator based on the comparison value. TheRF attenuator is configured to modify the amplitude of an RF inputsignal supplied to the power amplifier based at least in part on thereference signal.

In some embodiments, the RF attenuator can be a digital attenuatorconfigured to modify the amplitude of the RF input signal based at leastin part on an attenuation value. In some embodiments, the attenuationvalue can be a discrete attenuation value selected from a plurality ofdiscrete attenuation values. Selection of the discrete attenuation valuecan be based at least in part on the reference signal.

In some embodiments, the RF attenuator can be an analog attenuatorconfigured to modify the amplitude of the RF input signal based at leastin part on an attenuation value. In some embodiments, the attenuationvalue can be based at least in part on an analog voltage that iscontinuously modified until the reference signal indicates that thepower amplifier is not operating in a saturated state. In someembodiments, the analog attenuator can determine whether to modify theanalog voltage by increasing the analog voltage or decreasing the analogvoltage based at least in part on a polarity of the analog attenuator.

In accordance with some implementations, the present disclosure relatesto a wireless device including an antenna configured to at leasttransmit a signal from a transmitter, the signal being based at least inpart on a radio frequency input signal supplied to a power amplifier ofthe transmitter. The transmitter includes a power amplifier module. Thepower amplifier module includes the power amplifier and a poweramplifier bias controller. The power amplifier includes a cascodetransistor pair. The cascode transistor pair includes a first transistorand a second transistor. The power amplifier bias controller includes acurrent comparator, a saturation controller, and a RF attenuator. Thecurrent comparator is configured to compare a base current of the firsttransistor and a base current of the second transistor to obtain acomparison value. The saturation controller is configured to supply areference signal to the RF attenuator based on the comparison value. TheRF attenuator is configured to modify the amplitude of the RF inputsignal based at least in part on the reference signal.

In some embodiments, the RF attenuator can be a digital attenuatorconfigured to modify the amplitude of the RF input signal based at leastin part on a discrete attenuation value selected from a plurality ofdiscrete attenuation values. Selection of the discrete attenuation valuecan be based at least in part on the reference signal.

In some embodiments, the RF attenuator can be an analog attenuatorconfigured to modify the amplitude of the RF input signal based at leastin part on an attenuation value. The attenuation value can be based atleast in part on an analog voltage that is continuously modified untilthe reference signal indicates that the power amplifier is not operatingin a saturated state.

In accordance with some implementations, the present disclosure relatesto a power amplifier module including a power amplifier. The poweramplifier includes a cascode transistor pair. The cascode transistorpair includes a first transistor and a second transistor. The poweramplifier module includes a power amplifier bias controller. The poweramplifier bias controller includes a current comparator configured tocompare a first base current of the first transistor and a second basecurrent of the second transistor to obtain a comparison value. The poweramplifier module includes a saturation controller configured to supply areference signal to a voltage converter based on the comparison value.The voltage converter is configured to modify a supply voltage providedto the power amplifier based at least in part on the reference signal.

In some embodiments, the first transistor can be a common basetransistor and the second transistor can be a common emitter transistor.In some embodiments, the first transistor can be a common gatetransistor and the second transistor can be a common source transistor.

In some embodiments, the voltage converter can increase the supplyvoltage in response to the reference signal indicating that the firsttransistor is operating in a saturation region.

In some embodiments, the voltage converter can include a switch modeboost converter.

In some embodiments, the saturation controller can be further configuredto supply the reference signal to the voltage converter based on asecond comparison value corresponding to a second power amplifier. Insome embodiments, the voltage converter can be further configured tomodify a supply voltage provided to the second power amplifier based atleast in part on the reference signal.

In some embodiments, the saturation controller can further include adigital-to-analog converter and a ramp generator. The ramp generator canbe configured to supply a count value to the digital-to-analogconverter. The digital-to-analog converter can be configured to generatethe reference signal based at least in part on the count value.

In some embodiments, the saturation controller can include a pull-downresistor in electrical communication with the power amplifier biascontroller, a voltage input/output pin and a ramp clock generator. Theramp clock generator can be configured to detect whether the firsttransistor is operating in a saturation region based on a voltage acrossthe pull-down resistor. The voltage can be based at least in part on thecomparison value. The ramp clock generator can be configured to, inresponse to detecting that the first transistor is operating in thesaturation region, cause the ramp generator to modify the count value.

In some embodiments, the digital-to-analog converter can be furtherconfigured to generate the reference signal based at least in part on anaverage power tracking value. The average power tracking value can bedetermined based on a target power signal received from a base station.

In some embodiments, the voltage converter can be configured to modifythe supply voltage by boosting a battery voltage to a voltage level thatexceeds the battery voltage. In some embodiments, supply voltage can bebased at least in part on a battery voltage.

In accordance with some implementations, the present disclosure relatesto a transceiver including a receiver, a voltage converter configured tomodify a supply voltage provided to a power amplifier based at least inpart on a reference signal, and a transmitter. The transmitter includesa power amplifier module, a power amplifier bias controller, and asaturation controller. The power amplifier module includes the poweramplifier. The power amplifier includes a cascode transistor pair. Thecascode transistor pair includes a first transistor and a secondtransistor. The power amplifier bias controller includes a currentcomparator configured to compare a first base current of the firsttransistor and a second base current of the second transistor to obtaina comparison value. The saturation controller is configured to supplythe reference signal to the voltage converter based on the comparisonvalue.

In some embodiments, the voltage converter can increase the supplyvoltage in response to the reference signal indicating that the firsttransistor is operating in a saturation region.

In some embodiments, the saturation controller can be further configuredto supply the reference signal to the voltage converter based on asecond comparison value corresponding to a second power amplifier. Insome embodiments, the voltage converter can be further configured tomodify a supply voltage provided to the second power amplifier based atleast in part on the reference signal.

In some embodiments, the saturation controller can further include adigital-to-analog converter and a ramp generator. The ramp generator canbe configured to supply a count value to the digital-to-analogconverter. The digital-to-analog converter can be configured to generatethe reference signal based at least in part on the count value.

In some embodiments, the saturation controller can include a pull-downresistor in electrical communication with the power amplifier biascontroller, a voltage input/output pin, and a ramp clock generator. Theramp clock generator can be configured to detect whether the firsttransistor is operating in a saturation region based on a voltage acrossthe pull-down resistor. The voltage can be based on the comparisonvalue. The ramp block generator can be configured to, in response todetecting that the first transistor is operating in the saturationregion, cause the ramp generator to modify the count value.

In some embodiments, the digital-to-analog converter can be furtherconfigured to generate the reference signal based at least in part on anaverage power tracking value. The average power tracking value can bedetermined based on a target power signal received from a base station.

In some embodiments, the voltage converter includes a switch mode boostconverter.

In accordance with some implementations, the present disclosure relatesto a wireless device including a battery providing a battery voltage toone or more components of the wireless device and a transmitter. Thetransmitter includes a power amplifier module, a power amplifier biascontroller, and a saturation controller. The power amplifier moduleincludes a power amplifier. The power amplifier includes a cascodetransistor pair. The cascode transistor pair includes a first transistorand a second transistor. The power amplifier bias controller includes acurrent comparator configured to compare a first base current of thecommon base transistor and a second base current of the common emittertransistor to obtain a comparison value. The saturation controller isconfigured to supply a reference signal to a voltage converter based onthe comparison value. The voltage converter is configured to modify asupply voltage provided to the power amplifier based at least in part ona reference signal. The supply voltage is based at least in part on thebattery voltage.

In some embodiments, the wireless device can further include anon-volatile memory configured to store one or more average powertracking values corresponding to one or more target voltage values. Thesupply voltage can be based at least in part on an average powertracking value selected from the one or more average power trackingvalues. The average power tracking value can be selected based on atarget voltage from the one or more target voltage values.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

The present disclosure relates to U.S. patent application Ser. No.14/867,247, entitled COMPRESSION CONTROL THROUGH POWER AMPLIFIER LOADADJUSTMENT, and U.S. patent application Ser. No. 14/867,258, entitledCOMPRESSION CONTROL THROUGH AMPLITUDE ADJUSTMENT OF A RADIO FREQUENCYINPUT SIGNAL, filed on Sep. 28, 2015, and hereby incorporated byreference herein in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the drawings, reference numbers are re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate embodiments of the inventive subject matter described hereinand not to limit the scope thereof.

FIGS. 1A-1D illustrate graphs of simulations of an example poweramplifier using a cascode configuration.

FIG. 2 illustrates a first example of a portion of a transceiver thatincludes a cascode power amplifier and a saturation controller.

FIG. 3 illustrates an example of a saturation controller that can beused to prevent saturation of a cascode power amplifier.

FIG. 4 illustrates an example of a wireless device that includes a poweramplifier module.

FIG. 5 illustrates a second example of a portion of a transceiver thatincludes a cascode power amplifier and a saturation controller.

FIG. 6 illustrates a third example of a portion of a transceiver thatincludes a cascode power amplifier and a saturation controller.

FIG. 7 illustrates a flowchart of an embodiment of a saturationdetection and compensation process.

FIG. 8 illustrates an example of a timing diagram for saturationdetection and compensation.

FIG. 9 illustrates a graph comparing the base current for the commonbase transistor to the base current of the common emitter transistor ofa cascode power amplifier for a 2:1 VSWR (Voltage Standing Wave Ratio).

FIG. 10 illustrates a graph that depicts Adjacent Channel Leakage Ratio(ACLR) as a function of load for the 2:1 VSWR case of FIG. 9.

FIG. 11 illustrates a graph depicting the cases where saturation is notdetected when correlating the saturation detection and ACLR of FIGS. 9and 10 with embodiments described herein.

FIG. 12 illustrates a graph depicting the cases where saturation isdetected when correlating the saturation detection and ACLR of FIGS. 9and 10 with embodiments described herein.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

Introduction

Many wireless devices include one or more linear power amplifiers. Insome cases, the power amplifier receives a modulated waveform or signalthat includes amplitude modulated content. In order for the poweramplifier to accurately amplify the received signal before transmission,it is desirable to avoid compression of the signal. When the poweramplifier enters compression, the power amplifier output may no longerbe linearly related to its input. Once the power amplifier starts tocompress the signal and the device starts to enter a saturation mode,the modulated waveform may become distorted, which can result ininformation loss. Further the signal spectrum may change and start todegrade causing spectrum to spread into adjacent areas of the band andviolate system specifications. The spreading of the spectrum intoadjacent channels can interfere with other wireless devices therebynegatively impacting other wireless devices. This degradation may occurbecause a smaller version of the signal transmitted by the wirelessdevice with the power amplifier (PA) that is in compression occurs inspectrum allocated to another wireless device. This inner-modulationcomponent can be difficult to filter because it appears at a relativelysmall offset relative to the transmitted frequency. This offset istypically significantly closer to the carrier frequency than a harmonic.

Often, the power applied to the PA and the power compression point is afunction of the supply voltage and the load impedance. Thus, with afixed voltage supply and fixed load impedance, it is possible todetermine the saturated power level of the PA and the compressioncharacteristics of the PA. If the power amplifier is operating in asystem where the load impedance changes because, for example, theantenna or the antenna's environment changes (e.g., position of a user'shand relative to the antenna), then the compression and saturation pointof the PA can change. The power compression may result in the radiofrequency (RF) signal being clipped. Thus, the maximum amplitude of thesignal may be lost. Although it is often desirable to avoid compression,a PA is generally most efficient when operating near compression withoutdegrading spectrum. Thus, the PA often has a narrow operating range.

To address the problem of power compression, it can be desirable todetermine that a PA is operating in such a condition where the outputspectrum is degraded. This can be challenging because the degradedsignals can be approximately 30 db below a desired signal. One solutionis to use an RF detector or a receiver. However, adding an RF detectoror a receiver can add significant cost and may require a lot of currentresulting in shorter battery life for a wireless device. Further, addingthe additional components results in added complexity.

Embodiments herein can detect power compression by monitoring a Betavalue (referred to herein as “Beta”) for one or more transistors of thePA. Beta refers to a ratio between the collector current and the basecurrent of the transistor. Generally, the collector current is muchlarger than the base current. Thus, Beta is often between 100 and 120when the transistor is not in saturation. However, it should beunderstood that the Beta value for a transistor that is not insaturation may be both process and application specific. When Betadecreases, it can be determined that the transistor is in saturation.Often, the decrease in Beta will be relatively sharp, as illustrated forexample with respect to FIG. 1C. When the PA is significantlycompressed, Beta of the transistor may decrease to half of Beta in thenon-compressed stated.

One solution for monitoring Beta is to monitor the collector current andmonitor the base current for the one or more transistors and divide thetwo currents to obtain the current ratio, which would result in Beta.Monitoring the collector current may result in degrading or reducing theavailable power from the power supply available to the PA becausecomponents added to sense the collector current may reduce the availablepower. Thus, monitoring current can result in loss in the collectorfeed, which may result in the voltage presented to the collector of thePA transistor being reduced.

Embodiments presented herein reduce the impact of monitoring collectorcurrent on the available power by taking advantage of a cascodetransistor structure. FIGS. 2, 5, and 6, which are described in moredetail below, present several examples of systems that include a PA witha cascode configuration that may be used with embodiments describedherein.

FIGS. 1A-1D illustrate graphs of simulations of a power amplifier usinga cascode configuration that illustrates how Beta can be used to detectsaturation of the power amplifier, or the transistors thereof. FIG. 1Cis a graph 130 of Beta vs output power for the cascode transistor andfor the RF device transistor of a PA that is designed with a cascodeconfiguration. In this case, the cascode transistor may refer to thetransistor that is in electrical communication, although not necessarilydirect communication, with an antenna of a wireless device. Further, inthis case, the RF device transistor may refer to the transistor thatreceives an RF input signal for transmission.

As illustrated by the graph 130 in FIG. 1C, as the output power startsto compress, or the gain starts to compress, Beta starts to graduallyrise for each transistor before dropping off precipitously. However, asis clear from the graph 130, there is a 2 to 3 dB difference in theoutput power between the two transistors before the Beta decreasessharply. Thus, there is a significant difference in Beta when thecascode transistor first compresses or enters saturation.

Using embodiments disclosed herein, the saturation can be detected bycomparing Beta of the cascode transistor and Beta of the RF devicetransistor of the PA. As previously mentioned, there can be a largediscrepancy in Beta from one device to another device due tomanufacturing process, among other things. Thus, by determining arelative difference between the Beta values of two transistors, insteadof analyzing the Beta value of each transistor independently,embodiments presented herein may be process independent. In some cases,a difference in Beta of 20% may indicate saturation of the RF devicetransistor.

As illustrated by the graph 110 in FIG. 1A, the output power where thePA enters saturation is also roughly the point where the gain versusoutput power for the PA drops off. Further, as illustrated by the graph140 in FIG. 1D, when the PA enters saturation, the output power remainsconstant as the current increases. However, as with Beta, there is adiscrepancy between the base current of the cascode transistor and theRF device transistor. Thus, it is possible to compare the base currentsof the transistors of a PA with a cascode configuration instead ofcomparing the Beta values. Advantageously, in certain embodiments, bycomparing the base currents instead of the Beta values, the complexityof the hardware used to determine whether the PA is in saturation can bereduced and both cost and power savings can be achieved. Further, thegraph 120 of FIG. 1B illustrates that the ratio of the base currents forthe transistor pair that form the cascode PA can be used to identify thepoint at which the PA enters saturation.

Embodiments disclosed herein can determine that a power amplifier is incompression, or that a transistor of the power amplifier is operating ina saturated state, by analyzing the ratio of the base currents of a pairof transistors of the PA configured in a cascode design. The thresholdfor determining whether a transistor of the cascode transistor pair ofthe power amplifier is in saturation may be process and/or applicationspecific. For example, the threshold may be 1.2, or a difference of 20%.In some implementations, the threshold may be set or adjustable based onuser settings or an operating environment.

A number of implementations are possible for detecting whether the poweramplifier is in compression and for taking the power amplifier out ofcompression. Several embodiments are described herein with respect tothe remaining figures. Further, embodiments herein are describedprimarily with respect to a transmitter. However, it should beunderstood that some implementations of the systems described herein canbe adapted for use with a receiver.

First Example Transceiver

FIG. 2 illustrates a first example of a portion of a transceiver 200that includes a power amplifier module 202, which includes a cascodepower amplifier 208 and a saturation controller 240. In someimplementations, the transceiver 200 may be a transmitter. Generally,embodiments described herein are used with respect to transmitters. Itis often not necessary to implement the embodiments described hereinwith respect to a receiver because the receiver is typically designed tosupport a maximum expected receive signal and the supported compressionlevel with the receiver is generally much greater than with thetransmitter. However, the dynamic range of the receiver may also resultin a greater current drain. Thus, in some embodiments, embodimentsdescribed herein may be used with a receiver to reduce the dynamic rangeand to increase power savings. Accordingly, although embodimentsdescribed herein are generally described with respect to a transmitter,in some embodiments, the transceiver 200 may be a receiver. The cascodepower amplifier 208 is a power amplifier with transistors 210 and 212that are electrically connected in a cascode configuration. The cascodeconfiguration stacks one transistor 212 above the other transistor 210such that, in the case of bipolar junction transistors (BJTs), theemitter of the transistor 212 is in electrical communication with thecollector of the transistor 210. It should be understood that thecascode power amplifier 208 may be a part of a power amplifier 204. Forinstance, the cascode power amplifier 208 may be a portion of the PA 204that includes a pair of transistors in a cascode configuration.

The transistor 210 may be referred to as the RF device transistor or RFtransistor and is configured to receive a RF input signal. Thetransistor 212 may be referred to as the cascode transistor and isconfigured to provide a reference current that can be used by theamplifier bias controller 230 and/or the saturation controller 240 todetermine whether the transistor 210 is operating in a saturation mode.In some implementations, the transistors 210 and 212 are BJTs. In suchcases, the transistor 210 may be a common emitter transistor and thetransistor 212 may be a common base transistor. In other words, thetransistor 210 may have its emitter in electrical communication with acommon ground and the transistor 212 may have its base in electricalcommunication with the common ground (e.g., via a capacitor 214).Alternatively, the transistors 210 and 212 may be field effecttransistors (FETs). In some such cases, the transistor 210 may be acommon source transistor and the transistor 212 may be a common gatetransistor.

As illustrated in FIG. 2, the cascode power amplifier 208 may be part ofa power amplifier 204 that can include a number of additional devices.For example, the power amplifier 204 may include a bias circuit 206, acapacitor 216 in electrical communication with the base of the commonemitter transistor 210, a capacitor 214 in electrical communication withthe base of the common base transistor 212, and an inductor 250 inelectrical communication with the collector of the common basetransistor 212.

The capacitor 216 may be configured to prevent DC bias from leaking intothe load on the RF input. Further, the capacitor 214 can function as abypass capacitor configured to keep RF energy off of the node betweenthe bias circuit 206 and the base of the common base transistor 212. Theinductor 250 may be configured to supply a supply voltage to the cascodepower amplifier 208. The supply voltage may be provided to the collectorof the common base transistor 212.

The bias circuit 206 may include a circuit for providing a bias currentto the cascode power amplifier 208. In some embodiments, as illustratedin FIG. 2, the bias circuit 206 is included as part of the poweramplifier 204. However, in some other embodiments, the bias circuit 206may be separate from the power amplifier 204. The bias circuit 204 mayinclude a transistor 220 that may be configured to supply a voltage tothe base of the common emitter transistor 210. The transistor 220 mayact as a buffer and can supply the base current to the common emittertransistor 210. This base current may be based at least in part on avoltage generated by the RF bias block 224 that may be applied via thetransistor 220 to the common emitter transistor 210. The voltage thatmay be generated by the RF bias block 224 may be based on a current biasblock 232. This current bias block 232, which may be included as part ofthe power amplifier bias controller 230, may be a current source formedfrom a pair of diodes. In some cases, one of the diodes may beconfigured with a voltage that is equal to, or within a thresholddifference of, a base-emitter voltage (Vbe) of the common emittertransistor 210. The other diode may have a voltage that is equal to, orwithin a threshold difference of, a Vbe of the bias transistor 220.

Further, the bias circuit 204 may include a transistor 218 and a cascodebias block 222, which are configured and function similarly to thetransistor 220 and the RF bias block 224, respectively. In other words,the transistor 218 may be configured to supply a voltage to the base ofthe common base transistor 212. Further, the transistor 218 may act as abuffer and can supply the base current to the common base transistor212. This base current may be based at least in part on a voltagegenerated by the cascode bias block 222 that can be applied via thetransistor 218 to the common base transistor 212. The voltage that maybe generated by the cascode bias block 222 may be based on a currentbias block 234. Like the current bias block 232, the current bias block234, which may be included as part of the power amplifier biascontroller 230, may be a current source formed from a pair of diodes. Insome cases, one of the diodes may be configured with a voltage that isequal to, or within a threshold difference of, a Vbe of the common basetransistor 212. The other diode may have a voltage that is equal to, orwithin a threshold difference of, a Vbe of the bias transistor 218.

In addition to including the power amplifier 204, and in some cases, thebias circuit 206, which may be included in the power amplifier 204 ormay be a separate system, the power amplifier module 202 may include aPA bias controller 230. As described above, the PA bias controller 230may include a pair of current bias blocks 232 and 234 for providing biascurrents to the RF bias block 224 and the cascode bias block 222,respectively. Further, the PA bias controller 230 may include a currentcomparator 236 that can compare the collector currents of thetransistors 218 and 220.

With the cascode configuration of the cascode power amplifier 208, thecurrent may flow, in some implementations, through the common basetransistor 212, or the cascode device, from the collector to the emitterof the common base transistor 212. Further, the current may flow fromthe collector to the emitter of the lower device, or the common emittertransistor 210, which may be referred to as the RF transistor. Thus, insome implementations, the current flowing from the collector to theemitter may be identical or substantially the same (e.g., within athreshold current difference) for both transistors 210 and 212.

Advantageously, in certain embodiments, because the collector-emittercurrent (Ice) is the same for both transistors 210 and 212, saturationor compression of the common base transistor 212, or the cascodetransistor, can be determined without calculating Beta, thereby enablingsaturation or compression detection without the additional complexity ofadding Beta detection and measurement devices.

As discussed previously, Beta is equal to the collector current dividedby the base current. Further, the transistors 210 and 212 are configuredto have the same Beta, or to at least each have a Beta within athreshold difference of each other. Thus, as Beta of the cascode poweramplifier transistors 210 and 212 are equal and the collector current isequal, the base currents of the transistors 210 and 212 should be equal.Therefore, in some implementations, it is possible to detect when or ifthe common base transistor 212 enters saturation by comparing the basecurrents of the transistors 210 and 212 to determine if there is adiscrepancy between the base currents of the transistors 210 and 212that exceeds or satisfies a threshold discrepancy.

To compare the base currents of the transistors 210 and 212, the currentcomparator 236 may be provided with the base current of the transistor212 and the base current of the transistor 210. The base currents of thetransistors 210 and 212 may be the currents provided by the bias circuit206. Thus, the current ICsd, which is the collector-emitter current(Ice) of the transistor 218, and which drives the base of the commonbase transistor 212, is the effective base current of the transistor212. Further, the current IRF, which drives the base of the commonemitter transistor 210 and is the Ice of the transistor 220, can serveas the effective base current of the transistor 210. By comparing thecurrent ICsd and IRF using the current comparator 236, the PA biascontroller 230 can determine whether the transistor 212 is saturated.

When the PA 204 is not in compression, the currents ICsd and IRF will beequal, or have no more than a threshold difference. As the PA drivesinto compression, ICsd will typically increase relative to IRF. In suchcases, the current comparator 236 can detect the relative change incurrent and provide a signal to the saturation controller 240 indicatingthat the PA 204, or more specifically the cascode PA 208, is incompression. Typically, when the cascode PA 208 enters compression, thesignal spectrum degrades, which results in a degradation of systemperformance. Advantageously, in certain embodiments, by using the ICsdand IRF currents to detect compression, compression detection can besimplified because elements or devices for measuring and comparing Betacan be omitted from the transceiver 200 and/or the PAM 202.

To determine whether the transistor 212 is operating in a saturatedstate, it is desirable to compare the current ICsd to a current thatcorresponds to a transistor that is not in saturation. Thus, in someembodiments, it is desirable to maintain the transistor 210 in anon-saturated state to serve as a reference for determining whether thetransistor 212 is saturated. Generally, the voltage that is applied tothe transistor 210 may be related to the voltage that is applied to thebase of the common base transistor 212. In certain implementations, thevoltage applied to the base of the common base transistor 212 is 1.2volts higher than the voltage of the emitter. It should be understoodthat this voltage difference of 1.2 volts is process dependent and mayvary in other implementations. However, assuming a process that resultsin a 1.2 volt difference between the base and emitter of the common basetransistor 212, the voltage across the common emitter transistor 210 maybe 1.2 volts lower than the voltage applied to the base of the commonbase transistor 212. Thus, assuming sufficient biasing is applied by thebias circuit 206 at the base of the transistor 212 such that the node atthe base does not vary as a function of the received RF input or due tonoise, it can be assumed that the voltage across the common emittertransistor 210 will not saturate, or at least will not saturate prior todetection of saturation of the common base transistor 212. Therefore, byselecting the voltage that is applied at the base of the transistor 212and by selecting the capacitor 214, the transistor 210 can be preventedfrom saturating. In some embodiments, the transistor 210 may saturate ata higher power level than the transistor 212, thereby enabling detectionof compression by using the transistor 210 as a reference prior tosaturation of the transistor 212.

Upon determining that the power amplifier 204 has entered compression(e.g., that one of the transistors of the cascode PA 208 is insaturation) based at least in part on a comparison signal received fromthe current comparator 236, the saturation controller 240 can cause thesupply voltage applied to the power amplifier 204 to be modified. Forexample, the saturation controller 240 can cause the power amplifier 204to be taken out of a compression state by increasing the supply voltageapplied to the power amplifier 204.

In some embodiments, the saturation controller 240 can increase thesupply voltage by providing a reference signal to a boost converter,such as the switch mode boost converter 242. Based on the referencesignal, the switch mode boost converter 242 can adjust the supplyvoltage applied to the power amplifier 204. The supplied DC voltage setsthe headroom on the power amplifier 204. Thus, when the power amplifier204 is in compression, the switch mode boost converter 242 triggers anincrease in the DC supply voltage applied to the PA 204, which can takethe PA 204 out of a compression state and can correct its spectrum. Incertain embodiments, the boost converter 242 can be a buck converter.However, the boost converter 242 is not limited as such, and othervoltage or current modification converters can be used with embodimentsherein.

Although the saturation controller 240 is illustrated as an independentelement of the PAM 202, other embodiments are possible. For example thesaturation controller 240 may be part of the PA bias controller 230, theswitch mode boost converter 242, or separate from the PAM 202. Further,in some cases, the saturation controller 240 may be separate from thetransceiver 200. Similarly, although the switch mode boost converter 242is illustrated as an independent element within the transceiver 200,other embodiments are possible. For example, the switch mode boostconverter 242 may be integrated with the PA bias controller 230.

The saturation controller 240 is described in more detail with respectto FIG. 3. Further, as described in more detail with respect to FIGS. 5and 6, in some embodiments, the saturation controller may cause thepower amplifier 204 to be taken out of a compression state usingalternative or additional compression control processes.

The transceiver 200 may transmit a signal based on the RF input signalvia the antenna 246. Further, in some embodiments, one or more impedancematching, filter, and/or switching elements included in block 244 may bein electrical communication between the antenna 246 and the poweramplifier 204. As is described in more detail below, in someembodiments, the saturation controller 240 can take the power amplifier204 out of a state of compression by controlling an impedance matchingnetwork included in block 244 to modify a load applied to the poweramplifier 204.

In certain embodiments, each of the devices and/or circuits of thetransceiver 200 may be implemented using a common process or on the samedevice. However, in other embodiments, portions of the transceiver 200may be implemented using different processes. For example, the amplifierbias controller 230 may be implemented on a silicon die, while the poweramplifier 204 may be implemented using a difference material, such asgallium arsenide (GaAs).

Example Saturation Controller

FIG. 3 illustrates an example of a saturation controller 240 that may beused to prevent saturation of a cascode power amplifier 208. Aspreviously described with respect to FIG. 2, the saturation controller240 may receive a signal based on a comparison of currents from thecascode power amplifier 208. This signal may be received from thecurrent comparator 236. This received signal may be received at thesaturation feedback (SATFB) pin. Further, the saturation controller 240may output a reference signal that can be used by the switch mode boostconverter 242 to adjust a voltage supplied to the cascode poweramplifier 208.

The saturation controller 208 can include a radio frequency front end(RFFE) core 304, an 8 bit shadow register 306, an 8 bit ramp generator308, an 8 bit digital to analog converter (DAC) 310, a ramp clockgenerator 312 and an oscillator clock 314. Further, the saturationcontroller 208 may include a pull down resistor 316 that facilitatesdetermining whether one or more transistors 302 are in compression.

The RFFE core 304 can include an RFFE core that satisfies the MIPI®Specification from the MIPI® Alliance. The RFFE core 304 receives atarget voltage value for the PA 204 via a serial data (SData) pin, whichis clocked in via the serial clock (SCIk). Alternatively, the RFFE core304 receives a default value representative of the target voltage value.The target voltage, or the corresponding default value, may beidentified by accessing an average power table stored in a memory.Further, the target voltage may be selected based on a target powerlevel. This target power level may be specified by a base station thatis in communication with a wireless device that includes the transceiver200.

Once the RFFE core 304 receives the target voltage via the SData pin,the RFFE core 304 can convert the serial data into parallel data as an8-bit word, which can be stored in the 8-bit shadow register 306.Although described as an 8-bit word, other data sizes are possible.Further, the 8-bit devices may be of other sizes. For example, theshadow register may be a 16-bit shadow register configured to store a16-bit word or two 8-bit words.

The word stored in the 8-bit shadow register 306 can be used as aninitial or default state for an 8-bit counter. This 8-bit counter can bemaintained by the 8-bit ramp generator 308. The 8-bit counter may bedriven by a clock signal received from the ramp clock generator 312 thatbases its clock signal on the oscillator clock 314 and the signalprovided by the current comparator 236 (e.g., the SATFB signal).Advantageously, the 8-bit shadow register 306 enables the saturationcontroller to store data, e.g., an initial counter value correspondingto a target voltage value, while new data may be received at the RFFEcore 304 via the serial interface SDATA. Thus, in some cases, thesaturation controller 240 can control the transition timing between aprevious target voltage value and a new target voltage value preventinga time period without an initial counter value during a transitionperiod.

In certain embodiments, the saturation controller 240 may be sharedamong multiple PAs, transmitters, or transceivers as illustrated by themultiple transmit modules 302 in electrical communication with the SATFBline. Each of the transmit modules 302 may be configured similarly tothe transceiver 200 described with respect to FIG. 2. The saturationcontroller 240 can include a VIO pin, which may be a 1-pin interfacethat receives a digital logic high signal. If a power amplifier of anyof the transmit modules 302 goes into saturation, the signal receivedacross the SATFB can pull down resulting in a voltage across theresistor 316 causing a current to flow across the resistor andindicating to the ramp clock generator 312 that a PA is in saturation.

When the ramp clock generator 312 receives a signal indicating that a PAis in saturation, it can increment the ramp generator 308 one bit at atime by providing a clock signal to the ramp generator 308. In some suchcases, the ramp generator 308 serves as a counter that counts based onthe clock signal from the ramp clock generator 312 and the initial valueprovided by the shadow register 306. The incremented count value, insome cases, serves as the word, or data, that drives the DAC 310. TheDAC 310 can convert the digital counter value to an analog signal, whichmay be provided to a boost converter 242 to drive or modify the voltagesupply provided to the PA in saturation. Thus, in some cases, the DAC310 may output a reference signal that can be provided to a boostconverter (e.g., the boost converter 242), which can translate thereference signal into a voltage that may be applied to the collector ofthe transistor 212. This applied voltage may be referred to as a boostvoltage and can be used to increase the voltage range on the poweramplifier 204, thereby reducing or eliminating compression.

Alternatively, or in addition, the reference signal output by the DAC310 may be used to modify an amplitude of the RF input signal and/or theload applied to the PA as will be described further with respect toFIGS. 5 and 6. In some cases, when SATFB pulls low, the ramp generator308 starts incrementing one bit at a time, which can result inincrementing the supply voltage to the power amplifier. An exampletiming diagram for adjusting the supply voltage is described below withrespect to FIG. 8.

As described above, the initial count value corresponding to a boostlevel may be incremented when the PA 204 enters a compression state orhas a transistor in saturation. Once the PA 204 is taken out ofcompression, the boost state may be maintained. However, in some cases,the boost level may no longer be necessary because, for example, thewireless device has moved closer to the base station or the VoltageStanding Wave Ratio (VSWR) conditions have changed. In some such cases,it may be determined that there is a threshold amount of voltageheadroom beyond the voltage level of a signal to be transmitted. Inother words, in some cases, the voltage level of the signal may be morethan a threshold level lower than a maximum available voltage levelenabled by the boost. In such cases, the saturation controller 240 mayreset the counter for the boost value by providing a reset signal to theramp generator 308, thereby reducing the boost voltage. Moreover, insome such cases, a new default or initial value may be received at theRFFE core 304 corresponding to a new target voltage.

Example Wireless Device

FIG. 4 illustrates an example of a wireless device 400 that may includea power amplifier module 202 with a power amplifier 204 that includes apair of cascode configured transistors (e.g., the cascode poweramplifier 208). Although the wireless device 400 illustrates only onepower amplifier module (PAM), it is possible for the wireless device 400to include a number of PAMs, each of which may or may not be of the sameconfiguration as PAM 202. It should be understood that the wirelessdevice 400 is but one non-limiting example of a wireless device and thatother embodiments of the wireless device 400 are possible.

The power amplifier module 202 can include a number of elements. Theseelements may include, for example, a power amplifier 204 and a PA biascontroller 230. Each of these power amplifier module elements may beimplemented on the same circuit die. Alternatively, at least some of theelements of the power amplifier module 202 may be implemented on adifferent element circuit die. Advantageously, by implementing elementson a different circuit die, different semiconductor technologies may beused for different circuit elements of the power amplifier module 202.For example, the PA 204 may be implemented using gallium arsenide (GaAs)technology while the PA bias controller 230 may be implemented usingsilicon (Si).

As illustrated, the PA 204 may include a bias circuit 206 and the PAbias controller 230 may include a saturation controller 240.Alternatively, one or more of the bias circuit 206 and the saturationcontroller 240 may be separate elements included in the PAM 202.Further, although the PAM 202 is depicted as including a single PA 204,in some embodiments, the PAM 202 may include multiple PAs 204. Further,the PAM 202 may include a switching circuit, such as described withrespect to the block 244 of FIG. 2, which may be used to select a signalfrom among the plurality of PAs. The PAM 202 can facilitate, forexample, multi-band operation of the wireless device 400. The mode ofthe PAM 202 may, in some cases, be set by a power amplifier controller(not shown) based on a signal and/or mode selection set by thecontroller.

In some embodiments, the PA bias controller 230 may set the operatingpoint for the PA 204 by modifying the bias circuit 206. For instance,the PA bias controller 230 may set or modify a bias current provided bythe bias circuit 206 to the PA 204.

The power amplifier 204 may include any type of power amplifier.However, generally, the PA 204 includes a PA with a cascode transistorconfiguration as illustrated with respect to FIG. 2. Further, the PA 204may be set to operate at a particular operating point. This operatingpoint may be configured by the bias circuit 206, which may provide abias current and/or voltage to the power amplifier 204.

In some cases, the PAM 202 can receive RF signals from a transceiver 410that can be configured and operated in known manners to generate RFsignals to be amplified and transmitted, and to process receivedsignals. In some implementations, the PAM 202 is included as part of atransmitter 430, which may be included in the transceiver 410. In somesuch cases, the PAM 202 may process signals for transmission withoutprocessing received signals. In other implementations, the PAM 202 mayprocess both received signals and signals for transmission to, forexample, a base station.

The transceiver may further include a receiver 432 and a switch modeboost converter 242. The receiver 432 may include a separate PAM, or mayshare the PAM 202 with the transmitter 430. The switch mode boostconverter 242 may provide a boost voltage to the PAM 202. In some cases,the switch mode boost converter is included as part of the transmitter430 and/or the PAM 202.

The transceiver 410 may interact with a baseband subsystem 408 that isconfigured to provide conversion between data and/or voice signalssuitable for processing by one or more user interface elements and RFsignals suitable for processing by the transceiver 410. The transceiver410 may also be electrically connected to a power management component406 that is configured to manage power for the operation of the wirelessdevice. Such power management can also control operations of thebaseband sub-system 408 and the PAM 202. Further, the power managementcomponent 406 may provide a supply voltage to the switch mode boostconverter 242, which may boost the voltage before providing the voltageto the PA 204. It should also be understood that the power managementcomponent 406 may include a power supply, such as a battery.Alternatively, or in addition, one or more batteries may be separatecomponents within the wireless device 400.

A number of connections between the various components of the wirelessdevice 400 are possible, and are omitted from FIG. 4 for clarity ofillustration only and not to limit the disclosure. For example, thepower management component 406 may be electrically connected to thebaseband subsystem 408, the PAM 202, the DSP 412, or other components414. As a second example, the baseband subsystem 408 may be connected toa user interface processor 416 that may facilitate input and output ofvoice and/or data provided to and/or received from the user.

The baseband sub-system 408 can also be connected to a memory 418 thatmay be configured to store data and/or instructions to facilitate theoperation of the wireless device 400, and/or to provide storage ofinformation for the user. Further, in some embodiments, the memory 418may include an average power tracking (APT) table, or other datastructure. The APT table can identify target voltage levels for the PA204 that correspond to target power levels, which may be identified by abase station. For example, upon receipt of a target power level from abase station, the wireless device may access the APT table to determinea corresponding target voltage level. This target voltage level may beused to set an operating point for the PA 204.

In some embodiments, the call processor 434 may be in communication withthe base station. This call processor 434 may interpret commands fromthe base station and may access the APT table based on a commandreceived from the base station. Further, the call processor 434 mayinstruct the PAM 202 to adjust the operating point of the PA 204 byproviding the target voltage to a RFFE core of the saturation controller240, which may in turn adjust the voltage of the PA 204 by, for example,causing the boost converter 242 to boost the power supply voltage to thetarget voltage level identified in the APT table as corresponding to thetarget power level specified by the base station. An example ofadjusting the voltage level for the PA 204 is described in more detailbelow with respect to the timing example of FIG. 8.

In addition to the aforementioned components, the wireless device mayinclude one or more central processors 420. Each central processor 420may include one or more processor cores. Further, the wireless device400 may include one or more antennas 422A, 422B. In some cases, one ormore of the antennas of the wireless device 400 may be configured totransmit and/or receive at different frequencies or within differentfrequency ranges. Further, one or more of the antennas may be configuredto work with different wireless networks. Thus, for example, the antenna422A may be configured to transmit and receive signals over a 2Gnetwork, and the antenna 422B may be configured to transmit and receivesignals over a 3G network. In some cases, the antennas 422A and 422B mayboth be configured to transmit and receive signals over, for example, a2.5G network, but at different frequencies.

A number of other wireless device configurations can utilize one or morefeatures described herein. For example, a wireless device does not needto be a multi-band device. In another example, a wireless device caninclude additional antennas such as diversity antenna, and additionalconnectivity features such as Wi-Fi, Bluetooth, and GPS. Further, thewireless device 400 may include any number of additional components,such as analog to digital converters, digital to analog converters,graphics processing units, solid state drives, etc. Moreover, thewireless device 400 can include any type of device that may communicateover one or more wireless networks and that may include a PA 204 and/orPAM 202. For example, the wireless device 400 may be a cellular phone,including a smartphone or a dumbphone, a tablet, a laptop, a video gamedevice, a smart appliance, etc.

Second Example Transceiver

FIG. 5 illustrates a second example of a portion of a transceiver 500that includes a power amplifier module 202, which includes a cascodepower amplifier 208 and a saturation controller 240. In someembodiments, the transceiver 500 may be a transmitter. As illustrated bythe re-use of reference numerals, the transceiver 500 may include anumber of the elements of the transceiver 200. Further, elements of thetransceiver 500 that share a reference numeral with elements of thetransceiver 200 may include some or all of the embodiments describedwith respect to the transceiver 200. Thus, to simplify discussion,descriptions of elements of transceiver 500 that are similar to elementsof the transceiver 200 will not be repeated.

The transceiver 500 of FIG. 5 can identify whether the PA 204 is incompression in a similar manner as the transceiver 200 by comparing theICsd and IRF currents using the current comparator 236. However, ratherthan changing the supply voltage to increase voltage headroom of the PA204 to take the PA 204 out of compression, the saturation controller 240can use the output of the current comparator 236 to reduce the RF inputsignal provided to the PA 204 by use of an RF attenuator 502. Byreducing the RF input signal supplied to the PA 204, the output signalfrom the PA 204 is effectively reduced. If the output signal is reducedsufficiently, the PA 204 can be taken out of a compression operatingstate. Reducing the RF input signal may include reducing the amplitudeof the RF input signal.

In some cases, it is not desirable to reduce the RF input waveformbecause the signal provided to the transceiver 500 is reduced, which canresult in degraded performance. Using the transceiver 200 with thewireless device 400 may result in improved performance for the wirelessdevice 400; however, other wireless devices in communication with thesame base station as the wireless device 400 may have degradedperformance because the wireless device 400 is outputting a morepowerful signal, which may result in greater distortion for otherwireless devices. Using the transceiver 500 may improve the performanceof other wireless devices by reducing distortion, but may result inlower performance for the wireless device 400 due to the reduction inthe RF input signal. Thus, in some cases, the transceiver 200 may bepreferable when the wireless device 400 is farther from the base stationand the transceiver 500 may be preferable when the wireless device 400is closer to the base station. Advantageously, in certain embodiments,the systems of FIG. 2 and FIG. 5 can be combined. In other words, thewireless device 400 may increase the supply voltage and/or reduced theRF input signal based on operating conditions. Moreover, in some cases,the base station may provide a command to the wireless device 400 tocontrol whether the voltage supply and/or the RF input signal providedto the PA 204 is modified.

As illustrated in FIG. 5, the RF attenuator of the transceiver 500 maybe included as part of the PA bias controller 230. Alternatively, the RFattenuator 502 may be a separate element or included as part of the PA204. This RF attenuator 502 may be configured to receive the RF inputsignal and to attenuate the signal before it is provided to the poweramplifier 204. Generally, the RF input signal is a fixed signal.Further, it is generally desirable that the PA 204 not change the signalto prevent data loss. Thus, use of the RF attenuator 502 enables thefixed-input waveform to be provided to the PA 204, but with a loweramplitude, thereby reducing the occurrence of compression.

The RF attenuator 502 may be either a digital attenuator or an analogattenuator. In some embodiments where the RF attenuator 502 is a digitalattenuator, the RF attenuator 502 may include a number of discretevoltage levels. When the current comparator 236 detects saturation inthe PA 204, the saturation controller 240 can increment the attenuatorvalue and thereby decrease the RF input signal. In some cases, theattenuator value may be incremented iteratively based on the discretevoltage levels until the PA 204 is no longer operating in a state ofcompression.

In some embodiments where the RF attenuator 502 is an analog attenuator,an analog voltage sets the attenuation value. As saturation is detected,the voltage is adjusted, either ramped up or down depending upon thepolarity of the attenuator, such that the attenuation increases untilthe power into the PA 204 drops to remove the PA 204 from a state ofcompression. In other words, using the RF attenuator 502, the saturationcontroller 240 may increase the attenuation at a fixed rate untilcompression is eliminated in the PA 204. Once the current comparator 236indicates that the PA 204 is no longer in compression, the attenuationvalue may be held constant.

The RF attenuator 502 may include any type of circuit that can attenuatethe RF input signal while maintaining a constant impedance based atleast in part on a reference signal received from the saturationcontroller 240. In some embodiments, the RF attenuator 502 may include aPi-network and/or a T-network.

Third Example Transceiver

FIG. 6 illustrates a third example of a portion of a transceiver 600that includes a power amplifier module 202, which includes a cascodepower amplifier 208 and a saturation controller 240. In someembodiments, the transceiver 600 may be a transmitter. As illustrated bythe re-use of reference numerals, the transceiver 600, like thetransceiver 500, may include a number of the elements of the transceiver200. Further, elements of the transceiver 600 that share a referencenumeral with elements of the transceiver 200 may include some or all ofthe embodiments described with respect to the transceiver 200. Thus, tosimplify discussion, descriptions of elements of transceiver 600 thatare similar to elements of the transceiver 200 will not be repeated.

The transceiver 600 of FIG. 6 can identify whether the PA 204 is incompression in a similar manner as the transceivers 200 and 500 bycomparing the ICsd and IRF currents using the current comparator 236.However, instead of adjusting the supply voltage or attenuating the RFinput signal, the transceiver 600 can modify the load at the output ofthe PA 204. In certain embodiments, the block 244 can include animpedance matching network that can be controlled by the saturationcontroller 240. In such embodiments, the saturation controller 240 canprovide a reference signal to the impedance matching network of theblock 244 to modify the impedance at the output of the PA 204. Forexample, the saturation controller 240 can cause one or more switches ina switch capacitor based impedance matching network to be opened orclosed to modify the load at the output of the PA 204. In certainembodiments, by modifying the impedance load on the output of the PA204, the PA 204 can be taken out of compression.

As mentioned above, an impedance matching network may be electricallyconnected between the PA 204 and the antenna 246, and/or one or moreadditional devices. A variety of impedance matching networks may beutilized by the block 244. Examples of embodiments of an adjustableautomatic impedance matching network that may be used herein aredescribed in U.S. Provisional Application No. 62/057,451, filed on Sep.30, 2014 and titled AUTOMATIC IMPEDANCE MATCHING USING TRUE POWERINFORMATION, the entire disclosure of which is hereby incorporated byreference herein. Further, other adjustable load circuits may beutilized herein to modify the load of the PA 204.

In some embodiments, the load of the PA 204 and the voltage supply ofthe PA 204 may be modified in conjunction to remove the PA 204 from acompression state. In such embodiments, the saturation controller 240may provide a reference signal to both the switch mode boost converter242 and an impedance matching network of the block 244. Further, in someembodiments, the saturation controller 240 may be configured to adjustone or more of the voltage supply, the load of the PA 204, and anattenuation of the RF signal. Thus, in some implementations, thesaturation controller 240, and/or a base station, may use a combinationof techniques to prevent compression by the PA 204. In some embodiments,the selection of compression avoidance techniques may vary based on anoperating environment for the wireless device. For instance, in caseswhere the RF input signal is strong or have a power above a threshold,the saturation controller 240 may attenuate the RF input signal, but incases where the power of the RF input signal is below a threshold, thesaturation controller may adjust the voltage supply provided to the PA204 and/or the load of the PA 204. As another example, in cases wherethe base station determines that a number of wireless devices in aparticular geographic area are below a threshold, the base station maycause the wireless device to modify the voltage supply to preventcompression.

Example Saturation Detection and Compensation Process

FIG. 7 presents a flowchart of an embodiment of a saturation detectionand compensation process 700. The process 700 can be implemented by oneor more elements that can detect a power amplifier that is in a state ofsaturation causing compression of an RF input signal and that can modifyone or more operating conditions of the system to prevent the poweramplifier from being in the state of saturation. For example, theprocess 700, in whole or in part, can be implemented by a poweramplifier bias controller 230, a saturation controller 240, a switchmode boost converter 242, an RF attenuator 502, and/or an impedancematching network. Although any number of systems, in whole or in part,can implement the process 700, to simplify the discussion, portions ofthe process 700 will be described with reference to particular systems.

The process 700 begins at block 702 where, for example, the currentcomparator 236 monitors a base current (e.g., ICsd) of a common basetransistor 212 in a cascode power amplifier 208 of the power amplifier204. At block 704, the current comparator 236 monitors a base current(e.g., IRF) of a common emitter transistor 210 in the cascode poweramplifier 208. At block 706, the current comparator 236 compares thebase current of the common base transistor 212 to the base current ofthe common emitter transistor 210 to obtain a cascode PA current ratio.As previously described, the comparison of the base currents of thetransistors of the cascode PA 208 may be used to determine whether atransistor of the cascode PA 208 is in saturation, thereby indicatingwhether the PA 204 is in compression. Further, as previously described,in certain embodiments, by comparing the base currents of the cascode PA208 transistors instead of Beta, the PA 204 can be simplified, savingboth power and cost by eliminating elements to measure and compare Betato determine whether the PA 204 is in compression.

At decision block 708, the saturation controller 240 determines whetherthe cascode PA current ratio exceeds or satisfies a threshold. If not,the process 700 returns to block 702. If the cascode PA current ratioexceeds or satisfies the ratio, the saturation controller 240 at block710 modifies, or causes to be modified, at least one of the following:the DC supply voltage of the PA 204, the RF input signal supplied to thePA 204, and/or the load at the output of the PA 204. As previouslydescribed, a device may be configured to modify one, or more than one,of the DC supply voltage, the RF input signal, and/or the load at theoutput of the PA. In embodiments where the device can modify multipleoperating characteristics of the PA 204, the saturation controller 240may select whether to modify the supply voltage, RF input signal, and/orload of the PA 204 based on the operating environment of the wirelessdevice and/or based on a command from a base station.

Example Timing Diagram

FIG. 8 illustrates an example of a timing diagram for saturationdetection and compensation. Starting on the left side of the timingdiagram and at the bottom, a data input stream to the RFFE core 304 isillustrated. Each of the pulses may represent a serial-data stream. Anumber of operations may occur during each pulse and the timing diagramis simplified to generally illustrate that information is transferredover the RFFE bus to the PA. As indicated in FIG. 8, the first commandenables the boost supply from the boost converter 242. As a result, thetiming diagram illustrates that the boost output voltage begins to risesubsequent to the first pulse. Further, the boost RFFE Register 1 isprogrammed with the boost level, which may be determined form the APTtable. At the PA enable pulse, the PA 204 is activated and receives asupply voltage based on the DAC 310 output. Further, the PA 204 beginsto receive an RF input signal. Further, the timing diagram illustratesthat the PA 204 is not in saturation.

At point 802, an event occurs, such as the antenna impedance beingmodified, and results in the load to the PA 204 being adjusted. As aresult the PA 204 may begin compressing as a transistor of the PA 204begins to saturate. The saturation is illustrated in the timing diagramby the SATFB signal being pulled low.

In certain embodiments, the SATFB signal being pulled low triggers anincrease in the boost RFFE output. The ramp generator 308 is incrementedresulting in the reference signal from the DAC 310 being modified. Themodified reference signal may cause the boost converter 242 to increasethe supply voltage provided to the collector of the PA 204. The supplyvoltage may continue to increase until at some point the PA 204 comesout of saturation as illustrated at point 804. Once the PA 204 is nolonger saturated, the SATFB signal goes high signifying that thesaturation controller 240 can stop incrementing the collector voltage ofthe PA 204, or the boost output. In certain embodiments, the supplyvoltage is boosted, or is raised, above the battery voltage that isprovided to the PAM 202.

In the example timing diagram, once the PA 204 is out of saturation,everything remains constant until a point 806 a command is received toadjust the target power. This command may be received from the callprocessor 434 in response to a command received from the base station.In the illustrated example, the target power is reduced, which may occuras a wireless device moves closer to a base station. If the wirelessdevice were instead moving farther from the base station, the targetpower may be increased and the timing diagram may illustrate an increasein the voltage boost instead of a decrease. The base station may requestthat a wireless device modify its target power to prevent interferencewith other uses in communication with the base station. For example, ifthe base station is configured with to use Code Division Multiple Access(CDMA), which is a spread spectrum communication standard, multiplewireless devices may transmit at the same frequency using differentcodes. So that the base station can receive the signals from each of thewireless devices, it is desirable for the power levels to be roughlyequal. If a wireless device transmits at a much higher power level, thewireless device may act as a block to other wireless devices. Thus, itis desirable to maintain a constant power level.

In response to the request to reduce the target power, the wirelessdevice may access an APT table in the memory 418 to identify acorresponding target voltage for the target power and may cause thesaturation controller to adjust the boost accordingly so that the outputpower is reduced. Further, the RFFE core 304 may receive a new initialor default value, which is stored at the shadow register 306. If the PA204 begins to compress, the new initial value that is provided to thesaturation controller 240 is incremented using the ramp clock generator312 to adjust the reference signal provided by the saturation controller240 to adjust the supply voltage provided to the PA 204. Each time a newAPT value is received, the saturation controller 240 may be reset byproviding a reset signal to the ramp generator 308 and may receive a newdefault value at the RFFE core 304 corresponding to the target APTvoltage.

In certain embodiments, the transition to reduce power may take anon-zero amount of time. As such, during the voltage transition time,the modulation is ceased. This is illustrated by the flat line in the RFinput line of the timing diagram. The timing to adjust the voltage maybe small. For example, timing for the voltage adjustment may be on theorder of 25-microseconds. Once the timing window is over and the voltageadjustment is completed, the modulation is restored as illustrated inthe example timing diagram of FIG. 8. If the wireless device isdeactivated, or the wireless functionality of the device is deactivated(e.g., a non-transmission mode), the PA and voltage boost may bedeactivated as illustrated by the last two pulses in the timing diagram.

Simulation Results

FIG. 9-12 illustrate several graphs corresponding to simulationsperformed with a VSWR of 2:1 (or 2 to 1). The 2:1 VSWR value is oftenused for testing power amplifiers. FIG. 9 illustrates a graph 900 thatcompares the base current for the common base transistor to the basecurrent of the common emitter transistor of a cascode power amplifierfor a 2:1 VSWR. The graph 900 includes a number of lines that eachcorrespond to a different voltage level between Vcc of 11.5 volts forthe lowest line in the graph 900 and Vcc of 9 volts for the highest linein the graph. The ratio during which the PA is considered to be insaturation may vary based on process and specifications. For thisparticular simulation, saturation is determined to occur when there is a20% difference between the current values, or a ratio of 1.2. When thevoltage lines are above the 1.2 current ratio line 902, the simulated PAis considered to be saturated and when the voltage lines are below the1.2 current ratio line 902, the simulated PA is considered to be notsaturated.

FIG. 10 illustrates a graph 1000 that depicts Adjacent Channel LeakageRatio (ACLR) as a function of load for the 2:1 VSWR case of FIG. 9. TheACLR graph 1000 illustrates a measurement of spectrum in the channeldirectly adjacent to the spectrum utilized by a wireless device todetermine how much of the transmitted signal is leaking into thespectrum of another wireless device, or into the adjacent channel. Thedistortion that occurs when the PA 204 saturates may cause the spectrumof the wireless device to leak in to the spectrum of another wirelessdevice. For this particular simulation, saturation is determined tooccur when there is more −36 dB leakage (as illustrated by horizontalline 1002). Embodiments herein detect the spectrum leakage and reduce oreliminate the leakage by detecting PA compression and eliminating thecompression. The information of FIG. 9 can be crossed with theinformation of FIG. 10 to determine the effectiveness of embodimentsherein for detecting saturation and spectrum leakage across variousvoltage values for a simulated PA.

FIG. 11 illustrates a graph 1100 depicting the cases where saturation isnot detected when correlating the saturation detection and ACLR of FIGS.9 and 10 with embodiments described herein. As stated previously, whenthe current ratio is 1.2, or greater, the PA is considered to be incompression with a transistor of the PA operating in a state ofsaturation. The points on the graph 1100 are measurement points wheresaturation is not detected by a simulated saturation controller. Theline 1102 at −36 dB indicates the transition between when the simulatedPA is considered to be in saturation.

The Y-axis represents ACLR, and the horizontal line 1102 marked at −36dB represents the maximum acceptable adjacent channel leakage forrelease 99 of the 3^(rd) Generation Partnership Project (R99 3GPP)specification selected for the simulation. The R99 3GPP relates todevelopment of a 3G mobile phone system based on the Global System forMobile Communications (GSM) specification. The R99 3GPP specificationrequires that leakage into the adjacent channel does not occur anyhigher than −36 dBc. Each one of the symbols in the graph 1100 is ameasured data point for the ACLR where the current comparator 236 of thesimulated PA does not indicate saturation. Thus, during the simulation,the two base currents of the RF device and the cascode device weremeasured and compared. If the resultant comparison is less than 20% orthe ratio is less than 1.2, it is determined that the PA is not insaturation. In the graph 1100, each of the measured data points has aratio less than 1.2. The measured data points are correlated with theACLR. The different symbols used to indicate the measured data pointscorrespond to different voltage values between 9 volts and 11.5 voltsused for the simulation.

As previously mentioned, the line 1102 marks the threshold of maximumacceptable ACLR. As can be seen in the graph 1100, most of the pointsindicating that the PA is not in compression or saturated are below theline 1102 indicating acceptable ACLR when saturation is not detected.FIG. 12 illustrates a graph 1200 depicting the cases where saturation isdetected when correlating the saturation detection and ACLR of FIGS. 9and 10 with embodiments described herein. The line 1202 corresponds tothe line 1102 indicating the threshold for acceptable ACLR. The pointsillustrated in the graph 1200 indicate occurrences of saturation thatwere detected by the simulated saturation controller 240. In otherwords, points where the current comparator 236 determined that thecurrent ratio is greater than 20% of greater than 1.2. As illustrated inthe graph 1200, most of the points indicating PA compression are abovethe line 1202 indicating unacceptable ACLR when saturation is detected.

Thus, as can be seen by comparing the graphs 1100 and 1200, the graphsindicates that the simulated system can detect occurrences of saturationa majority of the time using the embodiments described herein to comparebase currents of the cascode PA. Once saturation is detected, one ormore of the embodiments described herein may be applied to take the PAout of saturation.

Terminology

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The term “coupled” is used to refer tothe connection between two elements, the term refers to two or moreelements that may be either directly connected, or connected by way ofone or more intermediate elements. Additionally, the words “herein,”“above,” “below,” and words of similar import, when used in thisapplication, shall refer to this application as a whole and not to anyparticular portions of this application. Where the context permits,words in the above Detailed Description using the singular or pluralnumber may also include the plural or singular number respectively. Theword “or” in reference to a list of two or more items, that word coversall of the following interpretations of the word: any of the items inthe list, all of the items in the list, and any combination of the itemsin the list.

The above detailed description of embodiments of the inventions are notintended to be exhaustive or to limit the inventions to the precise formdisclosed above. While specific embodiments of, and examples for, theinventions are described above for illustrative purposes, variousequivalent modifications are possible within the scope of theinventions, as those skilled in the relevant art will recognize. Forexample, while processes or blocks are presented in a given order,alternative embodiments may perform routines having steps, or employsystems having blocks, in a different order, and some processes orblocks may be deleted, moved, added, subdivided, combined, and/ormodified. Each of these processes or blocks may be implemented in avariety of different ways. Also, while processes or blocks are at timesshown as being performed in series, these processes or blocks mayinstead be performed in parallel, or may be performed at differenttimes.

The teachings of the inventions provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

Conditional language used herein, such as, among others, “can,” “might,”“may,” “e.g.,” and the like, unless specifically stated otherwise, orotherwise understood within the context as used, is generally intendedto convey that certain embodiments include, while other embodiments donot include, certain features, elements and/or states. Thus, suchconditional language is not generally intended to imply that features,elements and/or states are in any way required for one or moreembodiments or that one or more embodiments necessarily include logicfor deciding, with or without author input or prompting, whether thesefeatures, elements and/or states are included or are to be performed inany particular embodiment.

Disjunctive language such as the phrase “at least one of X, Y, or Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to present that an item, term, etc., may beeither X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z).Thus, such disjunctive language is not generally intended to, and shouldnot, imply that certain embodiments require at least one of X, at leastone of Y, or at least one of Z to each be present.

Unless otherwise explicitly stated, articles such as “a” or “an” shouldgenerally be interpreted to include one or more described items.Accordingly, phrases such as “a device configured to” are intended toinclude one or more recited devices. Such one or more recited devicescan also be collectively configured to carry out the stated recitations.For example, “a processor configured to carry out recitations A, B andC” can include a first processor configured to carry out recitation Aworking in conjunction with a second processor configured to carry outrecitations B and C.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A power amplifier module comprising: a poweramplifier including a cascode transistor pair, the cascode transistorpair including a first transistor and a second transistor; a currentcomparator configured to compare a first base current of the firsttransistor and a second base current of the second transistor togenerate a comparison signal; and a saturation controller configured tomaintain the power amplifier out of saturation based on the comparisonsignal.
 2. The power amplifier module of claim 1 wherein an emitter ofthe first transistor is coupled to a collector of the second transistor.3. The power amplifier module of claim 1 wherein the comparison signalindicates that the power amplifier is in a compression state.
 4. Thepower amplifier module of claim 1 wherein the comparison signalindicates a ratio between the first base current and the second basecurrent.
 5. The power amplifier module of claim 1 wherein the saturationcontroller is configured to supply a reference signal to a voltageconverter based on the comparison signal, the voltage converter beingconfigured to modify a supply voltage provided to the power amplifierbased at least in part on the reference signal.
 6. The power amplifiermodule of claim 1 wherein the saturation controller is configured tosupply a reference signal to an impedance matching network based on thecomparison signal, the impedance matching network being configured tomodify a load impedance of a load line in electrical communication withthe power amplifier based at least in part on the reference signal. 7.The power amplifier module of claim 1 wherein the saturation controlleris configured to supply a reference signal to an RF attenuator based onthe comparison signal, the RF attenuator being configured to modify theamplitude of an RF input signal supplied to the power amplifier based atleast in part on the reference signal.
 8. The power amplifier module ofclaim 1 wherein the saturation controller is configured to supply afirst reference signal based on the comparison signal to a firstoperating module and configured to supply a second reference signalbased on the comparison signal to a second operating module.
 9. Thepower amplifier module of claim 8 wherein the first operating moduleincludes a voltage converter configured to modify a supply voltageprovided to the power amplifier based at least in part on the firstreference signal and the second operating module includes an RFattenuator configured to modify the amplitude of an RF input signalsupplied to the power amplifier based at least in part on the secondreference signal.
 10. The power amplifier module of claim 8 wherein thefirst operating module includes a voltage converter configured to modifya supply voltage provided to the power amplifier based at least in parton the first reference signal and the second operating module includesan impedance matching network configured to modify a load impedance of aload line in electrical communication with the power amplifier based atleast in part on the reference signal.
 11. The power amplifier module ofclaim 1 wherein the saturation controller is configured to, based on apower of an RF input signal supplied to the power amplifier, supply afirst reference signal based on the comparison signal to a voltageconverter configured to modify a supply voltage provided to the poweramplifier based at least in part on the first reference signal or supplya second reference signal to an RF attenuator configured to modify theamplitude of the RF input signal based at least in part on the secondreference signal.
 12. The power amplifier module of claim 1 wherein thesaturation controller is configured to, based on a number of wirelessdevices in a particular geographical area, supply a first referencesignal based on the comparison signal to a voltage converter configuredto modify a supply voltage provided to the power amplifier based atleast in part on the first reference signal or supply a second referencesignal to an RF attenuator configured to modify the amplitude of an RFinput signal supplied to the power amplifier based at least in part onthe second reference signal.
 13. A method of maintaining a poweramplifier out of saturation, the method comprising: comparing a firstbase current of a first transistor of a cascode power amplifier and asecond base current of a second transistor of the cascode poweramplifier; and maintaining the cascode power amplifier out of saturationby modifying an operating characteristic of the cascode power amplifierbased on the comparison, the operating characteristic including a supplyvoltage provided to the cascode power amplifier, an amplitude of an RFinput signal supplied to the cascode power amplifier, or a loadimpedance of a load line in electrical communication with the cascodepower amplifier.
 14. The method of claim 13 wherein comparing the firstbase current and the second base current includes determining a ratio ofthe first base current and the second base current, maintaining thecascode power amplifier out of saturation including modifying theoperating characteristic based on the ratio.
 15. The method of claim 14wherein comparing the first base current and the second base currentincludes determining that the ratio of the first base current and thesecond base current exceeds a threshold, maintaining the cascode poweramplifier out of saturation including modifying the operatingcharacteristic based on the determination that the ratio of the firstbase current and the second base current exceeds the threshold.
 16. Themethod of claim 13 further comprising modifying a second operatingcharacteristic of the cascode power amplifier based on the comparisonsignal, the second operating characteristic including another of thesupply voltage, the amplitude of the RF input signal, or the loadimpedance.
 17. The method of claim 13 further comprising selecting theoperating characteristic based on an operating environment of thewireless device.
 18. The method of claim 13 further comprising selectingthe operating characteristic based on a command from a base station. 19.A wireless device comprising: a transceiver configured to generate an RFinput signal; a power amplifier module including a power amplifier, acurrent comparator, and a saturation controller, the power amplifierbeing configured to amplify the RF input signal to generate an RF outputsignal, the power amplifier including a cascode transistor pair, thecascode transistor pair including a first transistor and a secondtransistor, the current comparator being configured to compare a firstbase current of the first transistor and a second base current of thesecond transistor to generate a comparison signal, the saturationcontroller configured to maintain the power amplifier out of saturationbased on the comparison signal; and an antenna in communication with thepower amplifier module, the antenna configured to transmit the RF outputsignal.
 20. The wireless device of claim 19, the saturation controllerbeing configured to maintain the power amplifier out of saturation byproviding a reference signal to one or more of a voltage converter, anRF attenuator, or an impedance matching network, the voltage converterbeing configured to modify a supply voltage provided to the poweramplifier based at least in part on the reference signal, the RFattenuator being configured to modify the amplitude of the input RFsignal based at least in part on the reference signal, and the impedancematching network being configured to modify a load impedance of a loadline in electrical communication with the power amplifier based at leastin part on the reference signal.